If you want to change the color of your Pinata, use the Knups of plants. If you use the right plant Knups on a Pinata, it will change the color. For example, a Blue Bell to a Shellybean will change the color to blue. You can also make other species of Pinatas. For example, give your Sparromint a Buttercup Knup and it will change into a Candarie.
You can also make your Bunnycombs change to yellow if you make it eat a pumpkin.